The objective of this research proposal is to understand the role of activin in the control of pituitary FSH synthesis. Activin is produced by the pituitary where it regulates FSHbeta1 gene expression. Activin controls many other target tissues and functions including granulosa cell proliferation, theca cell steroid production, hematopoietic cell differentiation, and neuronal survival. By using one growth factor for a variety of physiological functions, organisms have limited the number of signaling pathways that are necessary for complex cellular functions and reduced the evolutionary pressure to devise larger genomes. Thus, the challenge is to understand how one factor, with a limited repertoire of signaling components, is able to selectively control such a broad array of gene activity. We hypothesize that the basis for the idiosyncratic response of each target cell to activin is due to pathway-specific transcription factors known as Smads, tissue-selective co-regulators, and the DNA promoter itself. Thus, activin can regulate the synthesis of FSH in the pituitary without turning on hemoglobin production in an inappropriate manner. The signaling pathway leading to regulated FSH production by the pituitary is the focus of this grant. Our preliminary studies identify the proximal 388 base pairs of the FSHb promoter as the activin-responsive region of the gene, establish a role for Smad3 in FSHb gene expression, and identify Pitx2 as a homeobox gene product involved in pituitary-specific FSH production. The central hypothesis that we will address is that activin controls gonadotrope function through the specific DNA and protein binding properties of Smad3 and Pitx2, and that these factors and their structural properties are essential to the regulation of FSH in vivo. There are three interrelated experimental aims in this proposal. The first two aims utilize molecular and biochemical approaches to investigate the mechanism of Smad3 and Pitx2 regulation of FSHb gene transcription. The last aim investigates the specific contribution of Pitx2 to pituitary FSH regulation using transgenic mice. These studies are expected to provide insight into tissue-restricted activin signaling and will contribute to a more complete understanding of normal fertility and the mechanisms that may underlie diseases in both men and women resulting from inappropriate pituitary FSH synthesis.